Pressure equalizing means for compressors and the like

ABSTRACT

A PRESSURE EQUALIZING DEVICE FOR A COMPRESSOR WHEREIN A VALVE CONTROLLED PASSAGE BETWEEN A HIGH PRESSURE CHAMBER AND A SUCTION CHAMBER OF THE COMPRESSOR IS PROVIDED FOR EQUALIZING THE PRESSURE IN THE SUCTION CHAMBER AND THE HIGH PRESSURE CHAMBER DURING START-UP OF THE COMPRESSOR. THE COMPRESSOR COMPRISES A ROTARY COMPRESSOR HAVING A ROTOR DISPOSED IN THE COMPRESSION CHAMBER FOR COMPRESSING FLUID SUCH AS REFRIGERANT FLUID WHICH IS PRECOOLED AND THEN DELIVERED TO THE HIGH PRESSURE CHAMBER FOR DELIVERY TO ASSOCIATED APPARATUS SUCH AS REFRIGERATION APPARATUS. THE FLUID IS RETURNED TO THE SUCTION CHAMBER OF THE COMPRESSOR THROUGH A RETURN INLET WHICH IS PROVIDED WITH A CHECK VALVE FOR PREVENTING REVERSE FLOW FROM THE SUCTION CHAMBER.

Sept. 20, 1971 B. w. ROMERHAUS PRESSURE EQUALIZING MEANS FOR COMPRESSORSAND THE LIKE Filed April 10, 1969 2 Sheets-Sheet l FIGI 'NVENTOR. BERTW. ROMERHAUS BY fi %J ll/gm,

ATTORNEYS.

Sept. 20, 1971 B. w. ROMERHAUS PRESSURE EQUALIZING MEANS FOR COMPRESSORSAND THE LIKE Filed April 10, 1969 2 Sheets-Sheet 2 FIG? FIG5

United States Patent 3,606,588 PRESSURE EQUALIZING MEANS FOR COMPRESSORSAND THE LIKE Bert W. Romerhaus, Haubstadt, Ind, assignor to WhirlpoolCorporation Filed Apr. 10, 1969, Ser. No. 814,908 Int. Cl. F04b 49/00US. Cl. 417292 5 Claims ABSTRACT OF THE DISCLOSURE A pressure equalizingdevice for a compressor wherein a valve controlled passage between ahigh pressure cham- -ber and a suction chamber of the compressor isprovided for equalizing the pressure in the suction chamber and the highpressure chamber during start-up of the compressor. The compressorcomprises a rotary compressor having a rotor disposed in the compressionchamber for compressing fluid such as refrigerant fluid which isprecooled and then delivered to the high pressure chamber for deliveryto associated apparatus such as refrigeration apparatus. The fluid isreturned to the suction chamber of the compressor through a return inletwhich is provided with a check valve for preventing reverse flow fromthe suction chamber.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to compressors and, in particular, to means for facilitatingstart-up of compressors such as rotary compressors.

Description of the prior art A number of pressure equalizing deviceshave been developed for use in rotary compressors such as employed inrefrigeration apparatus for compressing refrigeration fluid. In suchapparatus, repeated cycling places a severe strain on the compressormotor, and more specifically, places a severe strain on the motor duringstart-up of the compressor, when relatively high pressure differentialsoccur between the suction and discharge sides of the compressor.conventionally, split-phase motors are employed for use in such motorcompressors and thus, while the load requirements are such that a highstarting torque is desirable, such motors providing relatively lowstarting torque are severely strained by the high pressure differentialloading.

To provide improved use of such relatively low starting torque motors,devices for equalizing the pressure during a start-up of the compressorhave been developed. One example of such a pressure equalizing means isin my US. Pat. 3,348,764, owned by the assignee hereof, In that patent,a gravity biased valve member is provided for controlling communicationbetween the compressor inlet and outlet to equalize pressure across thecompressor during the start-up period. To provide a delayed action ofthe valve, a restriction is provided on the high pressure side thereof.In US. Letters Pat. No. 2,370,909, issued to Penn, an unloader device isprovided including a passage connecting the compressor inlet and outlet,a pivoted member, and a valve which is normally open during idle periodsand connected to the pivoted member for closing the unloading passage.The pivoted member is actuated by a magnetic means located adjacent themotor so as to be in the magnetic field of the motor when the motor isenergized, thereby to close the valve substantially immediately uponenergization of the motor and hold the valve closed throughout thecontinued energization of the motor.

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SUMMARY OF THE INVENTION The present invention comprehends an improvedpressure equalizing means replacing the gravity biased valve member ofmy earlier patent, and the magnetic operating means of the Penn patent,and providing a simple and economical control of the pressureequalization wherein the compressor is unloaded for a preselected periodat start-up. In the present invention, the pressure equalization periodis terminated as an incident of the compressor providing a preselectedrate of flow of the refrigerant fluid through a bypass whichautomatically closes the bypass. The bypass is caused to remain closedas an incident of the maintained pressure differential between the highpressure chamber and the suction chamber of the compressor.

More specifically, the invention comprehends a new and improved meansfor equalizing the pressure in the suction and high pressure chambersduring start-up of a compressor having a compression chamber, a suctionchamber, a high pressure chamber, and means for pumping fluid at highpressure from the pump chamber to the high pressure chamber. Thepressure equalizing means comprises a bypass passage providing directcommunication between the suction and high pressure chambers and flowcontrol means responsive to the mass flow of fluids from said highpressure chamber through the passage to the suction chamber to close thepassage as a result of the mass flow reaching a preselected value.

Further more specifically, the invention comprehends the provision ofsuch a pressure equalizing means wherein the flow control meanscomprises a reed valve.

Still further, the invention comprehends the provision of such apressure equalizing means wherein the flow control means includes meansfor maintaining the bypass passage closed as a result of the pressuredilferential between the high pressure chamber and the suction chamberof the compressor obtained after the start-up period.

Still further more specifically, the invention comprehends the provisionof such a pressure equalizing means wherein substantially all of thefluid circulated by the compressor during the start-up period isdelivered through the bypass passage to the suction chamber.

Still further more specifically, the invention comprehends the provisionof an improved reed valve for use as a pressure equalizing means in sucha compressor.

Further more specifically, the invention comprehends the provision ofsuch an improved reed valve which is responsive to the mass flow ofrefrigerant flowing therepast through a bypass passage. The mass flow isproportional to the velocity as well as the density of the refrigerant.The compressor herein is driven by a motor having a preselectedoperating torque characteristic so that upon closing of the equalizingvalve the motor will continue to accelerate to the desired operatingspeed.

The compressor motor generates sufiicient torque to cause a sufiicientmass flow to close the valve at a speed substantially less than thenormal operating speed of the motor. Where the compressor is operated atlow ambient temperatures, the motor generates sufiicient heat toincrease the vapor pressure of the refrigerant to effect the desiredclosing of the pressure equalizing valve.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages will beapparent from the specification and the drawings, in which:

FIG. 1 is a fragmentary vertical section of a compressor having pressureequalizing means embodying the invention;

FIG. 2 is a fragmentary enlarged horizontal section taken substantiallyalong the line 22 of FIG. 1;

FIG. 3 is a fragmentary horizontal section taken substantially along theline 33 of FIG. 1;

FIG. 4 is a fragmentary vertical section illustrating the closedarrangement of the reed valve;

FIG. 5 is a reduced horizontal section of the compressor takensubstantially along the line 55 of FIG. 1;

FIG. 6 is a fragmentary enlarged horizontal section of a compressorhaving a modified pressure equalizing means embodying the invention; and

FIG. 7 is a fragmentary vertical section taken substantially along theline 77 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the exemplary embodiment ofthe invention as disclosed in FIGS. 1 through 5 of the drawing, a motorcompressor generally designated 10 is shown to comprise a housing 11, acompressor 12 defined by a front head 13, a cylinder 14, a rear head 15,and a rotor 16. The front head 13 further defines a hub 17 carried on amotor shaft 18 which is rotatably driven by a conventional electricmotor (not shown). The front head 13, rear head and cylinder 14cooperatively define a compression chamber 19 in which the rotor 16 isrotatably disposed for compressing, in a conventional manner, a fluidsuch as refrigerant fluid through discharge ports 20 to a dischargechamber 21. The high pressure fluid may be precooled as by deliverythrough a line 22 to a precooler 23 and thence back into the highpressure chamber 24 of the housing 11. Such return to the housingpermits the cooled fluid to cool the compressor and thereby permitgreater efliciency in the operation thereof. The high pressure fluid isdelivered through an outlet 25 to the associated refrigeration apparatus(not shown) and is returned to the compressor throuugh an inlet tube 26which, as shown in FIG. 1, may be provided with a filter screen 27 and acheck valve 28. The inlet tube 26 opens to a suction chamber 29 whichcommunicates with the pump chamber 19 to complete the normal circuit ofthe fluid.

As discussed briefly above, the invention comprehends providing meansfor equalizing the pressure between the high pressure chamber 24 and thesuction chamber 29 during start-up of the compressor. As shown in FIG.1, the pressure equalizing means generally designated 30 comprises abypass passage 31 in the rear head 15 communicating with the highpressure chamber 24 and the suction chamber 29. As illustrated, thepassage 31 may comprise a right cylindrical passage providing directcommunication between the chambers 24 and 29. The passage 31 iscontrolled by a reed valve 32 which is carried on the rear head by meansof a pair of bolts 33. The reed valve 32 is spaced from the uppersurface 34 of the rear head 15 by a spacer 35 to dispose a movable valvemember portion 36 thereof slightly above the opening of the passage 31.As shown in FIG. 3, the valve member portion 36 is connected to a baseportion 37 of the valve 32 by a narrowed connecting portion 38. Theupper surface 34 of rear head 15 is provided with an annular depression39 coaxially about the opening 40 of passage 31 to define an annularvalve seat 41 coaxially of opening 40 and coplanar with surface 34. Arigid guard 42 is carried by bolts 33 outwardly of the valve 32 toprotect the reed valve 32 during assembly of the compressor.

More specifically, as shown in FIG. 4, valve 32 flexes to have the valvemember portion 36 seat coplanarly on the valve seat 41 by a flexing ofthe connecting portion 38 away from the guard 42. The flexing of thevalve is accomplished herein by the mass flow of the refrigerant fluidpast the valve member portion 36 into the passage opening 40 of thebypass passage 31 during the start-up of the compressor. The diameter ofthe passage 31 is preselected to assure a flow of substantially all ofthe refrigerant fluid being pumped by the rotor 16 during the start-upperiod, with weighed check valve 28 maintaining the return inlet tube 26closed at this time. Thus, during the start-up portion of the compressoroperation, the compressed refrigerant fluid is delivered from thecompression chamber 19 through the line 22 to the high pressure chamber24. The fluid then flows past the valve member portion 36 and throughbypass passage 31 directly back to the suction chamber 29 forrecirculation by the compressor rotor 16. However, when the rate of flowof the fluid past the valve member 36 reaches a preselected value, thedynamic forces generated by the fluid flow cause the valve member 36 tomove downwardly across the valve seat 41 to close the passage 31. Themass flow effecting the closing of the passage may be controlled bysuitably varying the parameters of the pressure equalizing system suchas the size of the valve member 36, the flexibility of the connectingportion 38, the resilient flex characteristic of the valve 32, the sizeof the passage 31, and the proximity of the valve member portion 36 tothe valve seat 41 in the open position.

As the operation of the reed valve 32 is controlled by the mass flow ofthe refrigerant, a variation in either the velocity or density of therefrigerant affects the operation of the valve. The density of such arefrigerant is related to the ambient temperature at the compressorhousing, and at low ambient temperature, such as approximately 0 F., the'vapor pressure of the refrigerant may be relatively low, such asapproximately 10 p.s.i.g. At such a low pressure the density of therefrigerant may be insuflicient to provide a sufiicient mass flow tocause a closing of the reed valve. However, suflicient heat is generated'by the drive motor to raise the temperature and pressure of therefrigerant, and thus the density thereof is sufiicient to provide amass flow suitable for closing the valve.

The speed of the compressor at which the valve closes is preferablysubstantially less than the normal operating speed of the compressor.Thus, after the valve is closed, the compressor accelerates to thedesired operating speed under increased load conditions, requiringsubstantially greater torque capabilities of the drive motor.

Illustratively, in one embodiment of the invention providing highlysatisfactory operation of the conpressor, the compressor cylinder had adiameter of 1.850 inches and a depth of .575 inch, and the rotor had adiameter of 1.593 inches. The compressor was driven by a conventionaltwo-pole, 3600 r.p.m. split-phase electric motor. The compressordisplaced in that compression approximately 2200 cubic inches per minuteof refrigerant fluid at the normal running speed of approximately 3600r.p.m. The valve 32 was formed of Swedish spring steel having athickness of approximately .005 inch. The valve member portion 36 had adiameter of approximately .312 inch, the connecting portion had a widthof approximately .09 inch, and the length of the connecting portion wasapproximately .308 inch. The spacer 35 had a thickness of approximately.05 inch, and the diameter of the passage 31 was approximately inch. Itwas found in such a compressor structure that the valve means 30effected a closing of the passage 31 at approximately 1500 r.p.m., orwhen the displacement of refrigerant by the compressor was approximately930 cubic inches per minute, as compared to a normal operating speed of3600 r.p.m., providing a displacement of approximately 2200 cubic inchesper minute.

After the valve member 36 seats on the valve seat 41, it is maintainedseated thereagainst by the pressure differential existing between thelow pressure fluid in suction chamber 29 and the high pressure fluid inchamber 24. When operation of the compressor is terminated, the valve 32returns to the normally open position of FIG. 1 in a short time (usuallyless than a minute), thereby opening the bypass passage 31 for equalizedpressure restarting of the compressor. The delay in the return of thevalve 32 to the open position is caused by the delayed reduction of thepressure differential across the valve to approximately 10 p.s.i.g. Thereduction in the pressure differential results only through leakage ofthe housing pressure through the bearing clearances and oil grooves pastthe rotor into the low-pressure cavity portion of the housing.

During the start-up of the compressor, only a small pressuredifferential occurs between the suction chamber 29 and the high-pressurechamber 24 as a result of the substantially direct communicationprovided by the passage 31. Illustratively, in a fractional horsepowercompressor the pressure differential may be of an order requiringapproximately .8 ounce feet of motor starting torque. Thus, the motor issubstantially completely unloaded during the start-up condition, wherebythe motor need only overcome the normal friction of the compressor andprovide the acceleration force to bring the compressor up to speed. Ahighly desirable feature of the present invention is the substantialelimination of underblade pressure during the start-up period, wherebythe rotor blades 43 (FIG. may ride over any excess oil accumulation inthe pump chamber 19.

Thus, the structure of claims 15 provides an improved pressureequalizing means which is extremely simple and economical ofconstruction while yet providing an effectively positive control of thepressure-equalized starting conditions of the motor compressor. Thepressure equalizing control is effectively removed from the system bythe pressure differential occurring during the normal operatingconditions of the compressor while yet the pressure equalizing systembecomes effective shortly after stopping the compressor.

Turning now to FIGS. 6 and 7, a modified form of pressure equalizingmeans generally designated 130 is shown to comprise a pressureequalizing means generally similar to pressure equalizing means 30 ofmotor compressor 10 but having a modified arrangement of the valve seatwherein the seat 141 is at an angle to the normal planar disposition ofthe reed valve 132. Thus, as shown in FIG. 7, the reed valve 132 merelyfiexes about the portion 144 secured by bolts 133 to have the distalportion 145 extend substantially parallel to the seat 141 at the time ofclosing. As further shown in FIG. 7, the bypass passage 131 extendsperpendicularly to the valve seat 141. In all other respects, thepressure equalizing means 130 is similar to the pressure equalizingmeans 30 and functions in a similar manner. Elements of pressureequalizing means 130 similar to those of pressure equalizing means 30are identified by similar reference numerals but 100 higher.

While I have shown and described one embodiment of my invention, it isto be understood that it is capable of many modifications. Changes,therefore, in the construction and arrangement may be made withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a compressor having means defining compression, suction andhigh-pressure chambers and means for pump ing fluid at high pressurefrom said compression chamber to said high-pressure chamber including anelectric drive motor, the improvement comprising: means for equalizingthe pressure in said suction and high-pressure chambers during start-upof the compressor, including means defining a bypass passage providingdirect communication between said suction and high-pressure chambers,and a reed valve disposed adjacent said bypass passage constructed tohave its physical arrangement changed as a result of mass flow of fluidtherepast from said high-pressure chamber into said bypass passage andthence to said suction chamber for closing said passage only when saidmass flow reaches a preselected value thereby permitting said motor tostart with substantially no pressure differential between said suctionand high-pressure chambers, said mass flow being a function of both thetemperature and volume rate or" flow of said fluid.

2. The pressure equalizing means of claim 1 wherein said reed valvecomprises means for closing said passage when said drive motor reachesat least approximately onethird normal running speed.

3. The pressure equalizing means of claim 1 wherein said reed valvefurther defines means for maintaining said bypass passage closed as aresult of the pressure differential between said high-pressure chamberand said suction chamber being maintained above a preselected minimumsubsequent to the closing thereby by said mass flow reaching saidpreselected value.

4. The pressure equalizing means of claim 1 wherein said flow controlmeans comprises a reed valve having a base portion secured to said meansdefining said bypass passage and an end portion cantilevered from saidbase portion to be normally spaced adjacent the inlet opening of saidbypass passage.

5. The pressure equalizing means of claim 1 wherein said bypass passagecomprises a right cylindrical passage opening toward said compressionchamber.

References Cited UNITED STATES PATENTS 1,965,420 7/ 1934 Lipman 230-222,169,131 8/ 1939 Albertson 23022X 2,284,980 6/ 1942 Mantle 230-22X2,536,995 1/1951 Hadley 23024 3,348,764 10/1967 Romerhaus 230223,358,908 12/1967 Garvin 23024 3,361,068 1/1968 Wochner 103-42 3,398,5518/ 1968 Yannascoli 103-42X 2,410,522 11/ 1946 Powell 417292X 3,313,5304/ 1967 Bickhaus 417292 WILLIAM L. FREECH, Primary Examiner US. Cl. X.R.417-299

